It's called "linguistic inference" and is the sign of a very smart child actually. It means that his understanding of the rules and roots of the language exceeds his years of experience with speaking it. Congratulations! :)

My username comes from the realization that most of my adult life has been spent surviving instead of LIVING. Sometimes I feel like a two dimensional object in a 3D world. It is my goal to correct whatever errors have put these feelings in me, by any means necessary. I aspire, now, to LIVE.